The regulation of the pyruvate and the branched chain alpha-keto acid dehydrogenases in cardiac tissue will be investigated. In the isolated perfused heart the effects of the perfusion conditions, alternative substrates, various hormones, and inhibitors of the mitochondrial monocarboxylate transporter on the regulation of pyruvate and branched chain enzyme complexes will be determined. The mechanism of the putative covalent modification of the branched chain alpha-keto acid dehydrogenase will be characterized. Further, factors controlling this activation/inactivation mechanism will be sought.